1. Field of the Invention
The present invention relates in general to mineral recovery wells, and in particular to a seal for sealing between wellbore members.
2. Brief Description of Related Art
In hydrocarbon production wells, a housing such as a wellhead housing or high pressure housing is located at the upper end of the well. The wellhead housing is a large tubular member having an axial bore extending through it. Casing will extend into the well and will be cemented in place. A tubing hanger, which is on the upper end of the casing, will land within the wellhead housing. The exterior of the tubing hanger is spaced from the bore of the wellhead housing by an annular clearance which provides a pocket for receiving an annulus seal.
There are many types of annulus seals, including rubber, rubber combined with metal, and metal-to-metal. One metal-to-metal seal in use has a U-shape, having inner and outer walls or legs separated from each other by an annular clearance. An energizing ring, which has smooth inner and outer diameters, is pressed into this clearance to force the legs apart to seal in engagement with the bore and with the exterior of the tubing hanger.
Some annular seals utilize wickers. Wickers may be located on the exterior of the tubing hanger, in the bore of the wellhead housing, or both. The outer leg of the seal embeds into the wickers of the bore while the inner leg of the seal embeds into the wickers of the tubing hanger. This locks the annulus seal in place, providing axial restraint, as well as forming a seal.
The sealing wickers are machined directly into the bore of the high pressure housing and landing subs or the neck of the tubing hangers. The annulus seal is made of a sufficiently deformable metal to allow it to deform against the wickers of the tubing hanger. The deformation occurs as the wickers “bite” into the annulus seal. In order to cause the seal to deform without damaging the wickers, the annulus seal is made of a metal that is softer than the steel used for the tubing hangers.
Debris, such as wellbore cuttings, may fill the wickers of the high pressure housing during standard drilling operations. Similarly, fluid such as drilling mud, water, or wellbore fluid may be present in the grooves of wickers on the high pressure housing and tubing hanger at the time the seal is set. The debris or fluid, collectively referred to as “fouling,” can develop a fluid pressure buildup, also referred to as hydraulic lock, and thus affect the sealing engagement between the annular seal and the sealing surface. It is desirable to be able to clear such fouling when the seal is energized.